Control system



1944. H. H. GORRIE 2,356,580

CONTROL SYSTEM Original Filed Dec. 3, 1938 2 Sheets-Sheet l "gnu i Q J a 80 l 2 8 l 2 so 5 3nnentor 2.: HARVARD H. GORRIE g Q PER CENT MOTOR SPEED TRANSMITTED mnousu ounma v Aug. 22, 1944. H. H. GORRIE CONTROL SYSTEM Original Fil ed Dec. 5, 1958 2 Sheets-Sheet 2 FIG. 2

- FINAL INITIAL CHANGE IN CONTROL PRESSURE I ,INITIAL CONTROL PRESSURE FINAL CONTROL PRESSURE 5 4 3 2 I o umnwwwml 023204 E u0Z IQ FIG. 3

TIME

FIGI 4 Innentor HARVARD H. GORRIE mmDwwwma JOKFZOO Z- Gttorneg TIME Patented Au 22, 1944 CONTROL SYSTEM Harvard H. Gorrie, Cleveland Heights, Ohio, as-

signor to Bailey Meter Company, a corporation of Delaware Original application December 3, 1938, Serial No.

243,892, now Patent No. 2,255,284, dated September 9, 1941. Divided and this application January 29, 1941, Serial No, 376,459 s 11 Claims.

. This invention relates to apparatus for con trolling the rate of output of variable ratio fluid transmission mechanisms, such as fluid, or more specifically hydraulic couplings. a

Such couplings are interposed between a constant speed source of power, suchfor'example as a synchronous motor, a turbine, or-Diesel engine,

and a preferably variable output driven device,

suchfor example as a fan, pump, or wheels of a vehicle; audit is specifically an object of my invention to'control the speed of the variable speed shaft of the coupling to maintain a desirable-rate r I of;-output of the driven device.

In some "cases the driven device may produce an agent directly or indirectly contributlngto. the production of or maintenance of a condition, such as temperature, pressure, level, rate of flow or electromotive force. My invention contemplates regulating the rate ofproduction of the agent by control of the coupling to maintain the condition at a desired predetermined value. Forexample," it is desirable to vary the rate of supply of the elements of combustion to a vapor generator in accordance with the demand for vapors as indicated by changes'in vapor pressure. In accordance with my invention the rate of output of the air and fuel supply means may-be varied to maintain a desired vapor pressure by control-1 ling a hydraulic coupling interposed between such means and their driving elements.

It is an object of 'my invention to provide a; couplingcontrol wherein-the actual output speedof the coupling follows promptly and accurately" W desired changes in the .speed without overtravel or hunting.

Another object of my invention is to provide a control system which will cause the actual rate of coupling output to correspond substantially e ing diaphragm motor valves H and I! normally disposedin a substantially closed position. When,

with the desired rate even during transient periods while the desired rate is changing.

Still another object of my invention is to provide a control system wherein the rate of change in coupling outputis determined in part by the magnitude of the change in output desired and in part by the rate of change in desired output.

A further object of my invention is to provide a control system .wherein' the rate of change in coupling output is varied in asymptotic relation- I in the coupling is caused to continuously. pass through a working circuit,-vwhich includes a cooler, such as I have illustrated .at 6. It will be noted that fluid'from the'coupling' passes through 9 a pipe 1 to the cooler! andis returned to the (Cl. sit-s4) Figs. 2, 3, 4 and 5am graphs illustrating operating characteristics of my control system. Fig. 6 is a sectional view to an enlarged scale of an adjustable bleed valve;

. =Ret'erring to Fig. 1, I have therein shown a hydraulic'ooupling- I adapted to receive power :irom an input shaft 2 and to deliver. power to a variable speed output shaft 3. The input shaft 2 may be driven: from any desiredsource of power, such as a'reciprocating'engine, electric motor, Diesel engine, steam turbine, or the like. For purposes ofdllustration I have shown it as being drivenby a multispeed motor- 4. Likewise the variable speed output shaft 3 is" adapted to actuate; a driven devlcesuch as a fan, pump, transmission system, stoker, ieeder, or in fact any power utilizing device. In theembodiment of -my invention I have chosen to describe I show theoutput shaft 3 as driving a fan 5.

20' .As known, the percent of the motor speed transmitted through the coupling varies in accordance with the amount of fluid in the coupling,

and changes in the speed oi-the output shaft may be made by varying the quantity of fluid in the coupling. To avoid overheating, the fluid used coupling through a-gpipe 8. l .A reservoir 9 is provided for excess fluid. When it is desired to increase the output. the coupling fluid is transferred'irom the reservoir to the, working crcuit' oi the coupling. Conversely, when.

itis desired to decrease the output of the cou- 1 pling fluid is transferred irqm the working circuit to the reservoir.- The means'I haveprovided for efiectingjtheftransfer oi fluid comprises a continuously operating pump l0, and oppositely actthe coupling output is constant, fluid drawn by to through a pressure regulating valve l3 anda pipe l4. Under the condition of constant cou-'- pling output a constant predetermined fluid pressure transmitted through a pipe I! is impressed on the diaphragm motors of valves II and I2 suflicient to hold them in the closed position; By

5 means hereinafter to be described when it is ,desired .to increase the coupling output some predetermined amount the fluid pressure is initially decreased correspondingly, thereby causing...the valve II to partially open whfle the valve: re--= V in fluid m w mm the esi s minsdnv l eo 5 A decreasginjcouplini output is: i f ected t ugh an increase in fluid pressure transmitted as the" diaphragm motors of valves II and I2, thereby causing the former to remain closed and the lat As I have indicated the coupling shown in Fig. 1 as driving a fan, as a measure of coupling output I may use the rate of fluid flow produced by the fan. Therein I show a fluid flow meter comprising a casing 24 divided into two chambers by a flxi'bledl'a 25 oorilrieeted by'ggpipesrii and fl 'toth fa'nt soas to lie-responsive :to a differentia-l varying in functional relation to the rate of fiid flow produced by the fan. It will be evident ter to open, withdrawing fluid from the W01'1iingfjf1Qwl3 those, skilled in the art that other factors circuit and returning it to th e reservo'ir. ,In gen- I era], it may be said thereforelth h ife determines the position of t and thereby effects transfer u the working circuit at a corresponding As will be apparent to those skilled in the art -the a k7 may be shaped 20 crank 23"will assume a predetermined position,

tion ibetw'een iii he control system therate o'f fair liowl lim ita I rather than difierential pressure may be used to coupling output. For exof the output shaft 3 may in more conveniently used than rsntia zmqaw by fluid flowiaphrag 5 "exerts a force on the bell c'fn 23i'act'in imopposition to the force exerted y tli bellows12 =I-I When the two forces are equal qn stand nin predetermined proportion, the bell which z for iconveniencefmay be, termed the snout'r'alpositionflf a a Movemen from the .neutra position will berpr xtiqna t the difference in forces ex rtedby the diaphragm 25aand ibellowsi ilwbyyy rue of aspringgn, so r iis dr hatiwh n .theip Produced-1hr. t e, bellows predominates the b ell crank 23 will be v between h beam-:19:sndmepowsaomyr'or convenience. a

plurality-"of"holes-fill in the beam 29 are shown; to'anyofwhich' thebellow's I DA may be connected. H H A The adjustable'bleed valve 33 1s shownin seccrease in coupling 'output'during the transition relationship between control pressure within the pipe ii'and timeupon an instantaneous displacement of the valve member i1 01' a predetermined amount. Curve B represents the relationship between control pressure and time when the same total displacement of the valve member l'l occurs. but which does not occur instantaneously. Curve. C represents the control pressure obtained when. the same total displacement of the member ll occurs over a still longer period of time, or at a slower rate. It will be noted" that as the rate of change in positionoifthe member change in control pressure It will thus be evident that upon rapid changes in the magnitude of the controlled condition my control system will operate to 'glvea relatively large and immediate change in rate of coupling output, whereas with relatively slow changes in the magnitude of the. controlled condition changes in coupling output will occur at a relatively, slower rate. Accordingly the rate of '20 i1 decreases the maximum initial likewise diminishes.

change of coupling output will correspond to the rate of change in; the magnitude oiJthe conv trolled condition.

It is sometimes impossible economicaliy'obtain the entire range in coupling'output desired with a single speed driving motorand it is therefore common practice to provide a motor havin two or more speeds and selectively determine the speed used in accordance with the rate of cou-- pling output. With the motor atlow speed, desired changes in coupling output are efiected by varying the volume of fluidin the coupling un'til it is substantially full of fluid, when a further desired increase in coupling output is effected by changing the speed oi the-driving means apre I determined amount. In orderitoprevent an excessive change in coupling output simultaneously with increase in motor speed, it is necessary to withdraw fluid from the c pling. -As the change incoupling. output occasioned by the change in motor speed occurs-at a relatively rapid rate, it is desirable to withdraw fluid from the coupling at a correspondinglyrapidrate, if a temporary change in outputoirelativelylarge magnitude during the transition period is to be avoided. In order to eflect the relatively rapid withdrawal oi iluid'necessary, I have found it desirable in addition to -the normal control means to provid additional control means operative during the transition period to effect a rapid withdrawal of fluid.

With the motor at high speed, decreases in coupling output are obtained by withdrawing fluid from the-coupling until it is substantially 7 empty, when the speed 01 the motor is decreased, and concurrently therewith the quantity of .fluid in the coupling increased. As'thetransitionpeis relatively long, the normal controimean :in

most instances can act rapidly enough to prevent .on. the same horizontal. line as period between high'and low motor speeds.

To preventthe motor speed from I changing, at times when the coupling output co-v incides with that output at which the speed of the motor is changed from low to high for example, itis desirable to provide a certain amount of overlap, that is to change the motor speed from low to high at a greater coupling output than the output at which the motor speed is reduced from high to low. In Fig. 51 have graphically illustrated the desired operation; With the motorat low; speed, changes in output are made by changingthe quantity .of fluid in the coupling until 'the point D is reached, when the coupling is substantially full of fluid. At this point the motor speed is.changed so that the percent of motor speed transmitted through the coupling is'reduced, Desirably during thistransition period the percent of maximum coupling output remains constant, so that'the point D is the point D. In order to obtain thisoperation during the transition period,- as hereinbei'orestated, it is necessary to withdraw fluid from; the working circuit of the coupling at a relatively rapid rate. With the motor on high speed, increases in coupling output are obtained through the normal control means by increasing the quantity :of fluid in the hydraulic coupling. Assuming the motor to be at high speed, decreases in coupling output are obtainedby decreasing the quantity of fluid inthe coupling until a point E is reached, when the motorspeed is reduced. Again it is desirable that pressure in the pipe 2| reaches predetermined values. The switch 50 is adjusted to close when a the percent of maximum coupling output at the reduced motor speed be the same as before the speed reduction. That is, that the point E lies on the same horizontal line as the point E. It will benoted that the point E is preferably not on the same horizontal linewith the point D, so that if the coupling output coincides with either of the points a continual changing of motor speed will not occur. The amount oi overlap provided can, of'course, be variedto suit the particular conditionsmet with in any given installation.

In the embodiment of my invention I haye shown at Fig. 1 the motor 4 is connected to a source A through a resistance 4|, thereby causing the motor to rotate at low speed. When it is desired to operatethe motor at high speed the resistance ll is shunted out. The resistance 4| has been shown as a means for changing the motor speed merely for simplicity and convenience. It will be evident from the explanation to follow that my controlsystem is not 'concemed in the coupling, and I may therefore eiiect, operation of the speed changing means when this pressure reaches predetermined values. Con-. nected to the pipe 2| are pressure switches 50 and II positioned to closed position when the the intcorres ondin to E- riod during which the motor speed is decreasing p0 p g E (Fig is reached. The switch Si is adjusted to operate when the point D-D' is reached. Thus it is the switch t! which determines the point of transition from low to high motor speed and the switch III which determines the point of transition iromhigh to low speed. Assuming that the at low speed, operation oi. the switch 7 motor I is continually f 50 has no effect upon motor speed. Upon further increase in pressure within the pipe 2| to a magnitude indicating that the coupling is substantially full of fluid, the switch 5| will close. As the switch 56 has previously closed, closure of switch 5| will effect energization of a solenoid 56, causing closure of flngers 51 and 58 operated thereby.- ,After initial energization of the solenoid 56, it will remain closed until switch 50 opens, as the circuit is completed through the holding finger 51'. v

Closure of finger 58 effects energization of a motor 59, causing it to rotate through spur gears 52-53, a shaft 60 carrying cams 6|, 62 and 63. Soon after the shaft 60 starts to rotate, cam 6| closes a switch 64 efiecting energization of a solenoid 65 operating a three-way valve 66 in the pipe IS. The valve 66, as shown, is in its normal position when pressures established by the pilot valve 3| are efiective for positioning the valves II and I2. Upon energization of the solenoid 65, however, the pressure established by the pilot valve 3| is rendered inefiective for pcsitioning the valves II and I2 and a fluid pressure of predetermined relatively high magnitude admitted through a pipe 66A is substituted therefor. The magnitude of this second fluid pressure is sufficient to cause the valve l2 to move to a wide open position, thereby causing fluid to be transferred from the working circuit of the coupling to the reservoir 9 at a maximum rate..

To further increase the rate at which fluid is withdrawn from the working circuit of the coupling I show disposed in the pipe I a three-way diaphragm motor actuated dump valve 61A'nor-' mally positioned to permit the free passage of fluid through the working circuit. The diaphragm motor of the valve 61A is connected to the pipe |5 through a pipe 68A and is arranged so that upon the predetermined pressure being made available by energization of the solenoid 65, it positions the valve 61A to prevent the circulation of fluid through the working circuit and direct all of the fluid to a pipe 69A leading to the reservoir 9. Energization of the solenoid 65 and consequent rapid removal of fluid from the working circuit will continue for substantially the entire revolution of the cam 6|.

Closure of switch 5| effects energization of solenoids 61 and 68, which thereafter will'remain energized until switch 56 is opened. A predetermined increment of time after switch 64 is closed a switch 69 is closed by cam 62, which shunts out the resistance 4| and causes the motor 4 to accelerate to high speed. The switch 69 carries an armature 10, which upon being positioned upwardly moves into the. magnetic field created by the solenoid 61 and looks the switch 69 in closed position for the duration of the energization of the solenoid. The motor 4 will therefore remain at high speed until the switch 5|) is opened.

The motor 59 is deenergized after the shaft 60' has made one revolution by the cam 63,'which shortly before the termination of the revolution causes cooperating contacts ll-12 to move upwardly. The contact 12 carries an armature 13, which is moved into the magnetic field of the solenoid 68 therebycausing its disengagement with the contact 1| upon further rotation of the cam and consequent stopping of the motor 59.

Deenergization of the solenoid 68 will cause re-- ngagement of contacts 1|12,so that the device is reset to starting position.

From the start of the motor 4 the sequence of events may be summarized as follows: As the coupling output increases the normal control will operate to vary the fluid volume in the couphng correspondingly. At the coupling output designated by the point E (Fig. 5) the switch will close. At the coupling output designated by the point D the switch 5| will close. Immediately thereafter valve l2 will be opened wide and valve 61A positioned to dump fluid from the coupling working circuit to the reservoir 9. A predetermined increment of time thereafter the resistance 4| will be shunted out and the. motor accelerated to high speed. After a further predetermined increment of time the valves II and I2 will be returned to normal control from the pilot valve 3|, and the valve 61A will be positioned so that fluid is again allowed to circulate through the working circuit of the coupling.

-By varying the length of the land of the cam 6| it is evident that I may vary the time period during which the valve I2 is opened wide and the valve 61A positioned to dump fluid into the reservoir 9. Likewise by changing the position of the land on the cam 62 the increment of time preceding the actual acceleration of the motor 4 and during which the valves I2 and 61A are positioned to a wide open position may be varied. Likewise I may vary the total time period during which the solenoid 65 is energized by changing the ratio of the spur gears 52-53 or speed of the motor, 59.,

Upon a decrease in coupling output the motor will stay on high speed until the point E (Fig. 5) is reached, when the shunt circuit will be broken through opening of switch 50 and consequent deenergization of solenoid 61. The motor will then decelerate to low speed. A hereinbeiore stated,

because of the longer transition period during which the motor speed is being reduced, I have found it is usually not necessary to provide other than the normal control means to increase the volume of fluid in the coupling to maintain the output substantially constant throughout that period. Reference to Fig. 1 will indicate that any change in the actual coupling output as indicated by the metering device 24 from the desired coupling output, as indicated by the pressure within the pipe 2| or force produced by the .bellows 22 will result in a change in the actual coupling output to restore correspondence with that desired. Thus during deceleration periods of the motor 4 the force produced by the diaphragm 25 will become less, due to the decrease in actual coupling output, and cause the valve member 30 to move downwardly, thus decreasing the pressure within the pipe l5, resulting in the valve opening and permitting fluid to enter the coupling, thus tending to restore the actual rate of coupling output to that desired. Usually the deceleration period is sufllciently long so that the actual coupling output will not depart from that desired an appreciable amount. In some instances, however, depending upon the j type of speed changing'mechanism employed, 1

normal deenergized position, as shown, the valve permits the free passage of fluid pressurethrough the pipe I5. During periods of deceleration the solenoid is energized, causing its associated valve member to move upwardly and vent the fluid pressure impressed on the motors of the valves II, I2 and 61 to atmosphere. The valve II is so designed that under this condition it opens wide 50 that fluid is introduced into the coupling at a maximum rate. As energization of the solenoid valve I is only momentary, I provide a suitable time delay means, such as a dashpot indicated at H, so that the length of time that the motors of the valves II, l2 and 61A are in communication with the atmosphere may be made to correspond in anyv desired way with the deceleration period of the motor 4.

The solenoid valve I00 is energized by closure of a normally open pivotally mounted mercury switch I02. Closure of the switch at the proper instant is obtained by providing the movable switch member of the solenoid 56 with a horizontal foot piece I03, which is arranged to strike an actuator I04 in its downward stroke and cause momentary tilting of the mercury switch in a counterclockwise direction, which then returns to the normal position by gravity. As hereinbefore explained, deenergization oi the solenoid 55 effects deceleration of the motor 4, so that at the instant of deceleration the solenoid valve I00 will be energized and the motors of valves II, i2 and 61A brought into communication with the atmos-' cation Serial No. 243,892 filed December 3, 1938,

now Patent 2,255,284, issued September 9, 1941 and copending.

What I claim as new, and desire to secure by Letters Patent of the United States, is:

1. A control apparatus for a hydraulic coupling of the type having an input and an output shaft and containing a volume of fluid, with means to vary the volume of fluid to produce desired changes in coupling output comprising means for initially changing the volume of fluid in the coupling at a, relatively rapid rate, and means responsive to said first named means for gradually reducing the rate of change of fluid volume to a lesser rate, the improvement in said control apparatus of means responsive to'the actual coupling output for diminishing the rate of change of fluid volume to zero as the actual rate of coupling output approaches the desired rate. v

2. A control system of the type for varying the volume of fluid in a hydraulic coupling to produce a desired change in coupling output, comprislng,'means for initially varying the volume of fluid in the coupling at a rate corresponding to the change desired, the improvement in said control system of means conjointly responsive to said first named means and to the actual rate of coupling output for thereafter modifying the 3. A control system of the type for varying the volume of fluid in a hydraulic coupling to produce a desired change in coupling output, comprising means for initially varying the volume of fluid in the coupling at a relatively rapid rate in a sense to effect the desired change in coupling output, the improvement in said system of means responsive to said flrst named means for thereafter gradually diminishing the rate of change in fluid volume independently of any change in the actual rate of coupling output.

4. A control apparatus for a hydraulic coupling of the type having an input and an output shaft and containing a volume of fluid, with means to vary the volume of fluid to produce a desired variation in coupling output comprising means for initially producing a change in a fluid pressure from an original value in sense and amount corresponding to the change in output desired, and means responsive to the fluid pressure for producing a gradual change in predetermined amount inthe fluid pressure in opposite sense, the improvement in said control apparatus of means for varying the volume of fluid in the hydraulic coupling at a rate corresponding to the magnitude of the fluid pressure, and means directly responsive to the actual rate of coupling output for returning said fluid pressure to the original value as the desired-change is consummated. 1

5. A control system of the type for varying the volume of fluid in hydraulic coupling to produce a desired change in coupling output, said control system including, a pilot valve having a movable member adapted to set up a control pressure corresponding in magnitude to the displacement of the member from a neutral position, means for initially displacing the member from the neutral position an amount corresponding tothe change in coupling output desired, an expansible'contractible chamber disposed in opposed relationship to said first named means adapted to position said member, a restricted connection between said'valve and chamber so that initial changes in said control pressure acting through said restricted connection within said expansible contractible chamber eflect a gradual continuing change in said control pressure in opposite sense to the original change, and valve means actuated by the fluid pressure for varying the rate of change of fluid volume in the hydraulic coupling in correspondence with the magnitude of the fluid pressure.

6. A control system of the type for varying the volume of fluid in a hydraulic coupling to produce a desired change in coupling output, said control system comprising means including a pilot valve having relatively movable elements and adapted to produce changes in a control pressure from a neutral value corresponding to changes in the relative positions of said elements from a predetermined relative position, means for relatively moving said elements in a direction and rate of variation in the volume of fluid in the j coupling so that the rate gradually diminishes to zero as the actual rate of output'approaches the desired rate.

extent to efiect an initially relatively large change in the .control pressure in a sense corresponding tively movin said elements in opposite direction to partially neutralize the initial change in control pressure, means for eflecting the change in the pressure acting on said pressure sensitive follow-up means in slow response to a change in the control pressure, and meansresponsive to the control pressure for varying the volume of fluid duce a desired change in coupling output, said control system including a pilot valve havin a movable valve member for producing changes in a fluid pressure proportional to changes in the position of said member, control means for initially moving said valve member in a direction and extent to efiect an initially relatively large change in the fluid pressure in sense corresponding to the desired direction of change in the coupling output, pressure sensitive follow-up means to give a reverse movement to said movable valve member directly responsive to the fluid pressure comprising an expansible chamber including a wall portion, moving in response to changes in fluid pressure in said expansible chamber and the movements of which position said valve member to give a change in the fluid pressure partially neutralizing the initial change in the fluid pressure produced by said control means, means for delaying the response of said follow-up means to changes in the fluid pressure comprising a restricted connection through which the pressure fluid seeps in passing to and from said expansible chamber, and means responsive to the fluid pres sure for varying the volume of fluid in the hydraulic coupling at a rate corresponding to the change in the fluid pressure so that the rate of coupling output is initially varied at a relatively rapid rate and then at a gradually diminishing rate as said pressure sensitive follow-up means gradually acts to diminish the initial change in the fluid pressure.

8. A control system of the type for varying the volume of fluid in a hydraulic coupling to produce a desired change in coupling output, said control system comprising means including a pilot valve having relatively movable elements .adapted to produce changes in a control pressure from a neutral value corresponding to changes in the relative positions of said elements from a predetermined relative position, control means for relatively moving said elements in a direction and extent corresponding to the desired direction of change in the coupling output and inamount corresponding to the amount of change in coupling output desired, pressure sensitive follow-up means directly responsive to the control pressure for relatively moving said elements in opposite direction to partially neutralize the initial change in control pressure, means for efiecting the change in the pressure acting on said pressure sensitive follow-up means in slow response to a change in the control pressure, means responsive to the control pressure for varying the volume of fluid in the hydraulic coupling at a rate corresponding to the difference between the actual value of the control pressure and theneutral value thereof so that the rate of coupling output is initially varied at a relatively rapid rate and then at a gradually diminishing rate as said follow-up means gradually acts to diminish the initial change in control pressure, means responsive to the actual rate of coupling output and a second follow-up means actuated by said last named means for relatively moving said elements in accordance with the actual rate of coupling output and acting to restore said relatively movable elements to said predetermined relative position when the actual change in coupling output corresponds to the desired change in coupling output.

9. A control system of the typefor varying the volume of fluid in a hydraulic coupling to produce adesired change in coupling output, said control system comprising means including a pilot valve having relatively movable elements and adapted to produce changes in a control pressure from a neutral value proportional to changes in the relative positions of said elements from a predetermined relative position, means for varying the volume of fluid in the hydraulic coupling at a rate proportional to the change in control pressure from the neutral value, control means for relatively movingsaid elements in a direction and extent proportional to the desired change in-coupling output so that a change in control pressure is produced proportional in magnitude to the change in coupling output desired and the volume of fluid in the hydraulic coupling varied at a rate proportional to said change, a first follow-up means directly responsive to said change in control pressure for relatively positioning said elements in the oppositev direction to partially neutralize the change in ,control pressure so that the volume of fluid in the hydraulic couplin is varied at a lesser rate, and a second follow-up means responsive to the actual rate of coupling output for relatively moving said elements in the same direction as said flrst follow-up means so that said elements are returned to said predetermined relative position when the actual change in coupling output corresponds to the desired change in coupling output.

10. A contro1 apparatus for a hydraulic coupling of the type having an input and an output shaft and .containing a volume of fluid with means to vary the volume of fluid to produce desired changes in coupling output comprising and mean for producing a control force corresponding to the desired coupling output, the improvement in said control apparatus of means for determining actual rate of coupling output, means actuated by said last named means for producing a control force proportional to the actual rate of coupling output, means for establishing a control effect proportional in magnitude to the difference in said forces, means for varying the volume of fluid in said hydraulic coupling at a rate corresponding to the magnitude of said control eifect, and means directly responsive to said control effect for gradually diminishing the magnitude thereof for a given difierence in said control forces so that upon an unbalance of said forces the volume of fluid in the hydraulic coupling is initially varied at a relatively rapid rate and then at a gradually diminishing rate.

11. A fluid pressure actuated superintendence apparatus for use with a hydraulic coupling for controlling the volume of fluid therein and for varying the rate of application of a corrective agent to maintain a control quantity at a desired value, comprising a pilot valve, a movable valve member for said pilot valve to establish a fluid pressure corresponding to the position thereof relative to said pilot valve, and operating means for said valve member comprising a lever pivotvalve member by the other, one of said connections being jointly movable by means responsive to the magnitude of the control quantity and means responsive to the actual rate of application of the corrective agent, and means by which the otherconnection is moved responsive to the fluid pressure established by said pilot valve and comprising an expansible chamber having a wall portion movable in response to changes in pressure in said chamber and operatively connected to said other connection, and means for retarding movements of said wall portion comprising a'restricted connectionthrough which the fluid pressure seeps in passing to and from said expansible chamber.

- HARVARD H. GORRIE; 

